The detection of Mycobacterium tuberculosis in respiratory bioaerosol of tuberculosis infected individuals

This thesis explores innovative methodologies for detecting aerosolized Mycobacterium tuberculosis (Mtb) in exhaled breath. The sensitivity of these methods was optimised by focusing on maximising aerosol production, aerosol capture and bacillus detection. Detection of aerosolised Mtb was then attempted across a broad spectrum of tuberculosis (TB) disease presentations. Initial studies using the respiratory aerosol sampling chamber (RASC) revealed culturable Mtb in 15 of 35 (42%) individuals with Xpert MTB-positive sputum, independent of sputum smear status or pulmonary cavitation. Enhanced sensitivity of the whole system culminated in a bioaerosol detection yield of >90% in Xpert MTB-positive sputum individuals. A key finding was the ability to detect Mtb in respiratory aerosols independently of coughing. Subsequent studies expanded sampling to diverse patient groups, including individuals without TB diagnoses. Unexpectedly high (>90%) Mtb detection rates across all groups prompted longitudinal monitoring, revealing bioaerosol positivity reductions concurrent with symptom resolution and, notably, independent of treatment. Parallel analyses found poor culturability of captured Mtb but confirmation through PCR for the Mtb-specific RD9 target and in 3 cases though genomic sequencing which identified distinct Mtb lineages. This result was further explored in a Bayesian modelling study which quantified Mtb exposure in the high TB burden community where this aerosol sampling was performed. This estimated an annual exposure rate of 5.1 episodes per individual, far exceeding established infection rates from immunoreactivity assays. These findings suggest rapid cycling of bioaerosol Mtb carriage and clearance within populations. These findings challenge traditional TB transmission paradigms with potentially significant public health implications.